Multiplexed multichannel photodetector

ABSTRACT

A light detection and ranging (LIDAR) system can emit light toward an environment and detect responsively reflected light to determine a distance to one or more points in the environment. The reflected light can be detected by a plurality of plurality of photodiodes that are reverse-biased using a high voltage. Signals from the plurality of reverse-biased photodiodes can be amplified by respective transistors and applied to an analog-to-digital converter (ADC). The signal from a particular photodiode can be applied to the ADC by biasing a respective transistor corresponding to the particular photodiode while not biasing transistors corresponding to other photodiodes. The gain of each photodiode/transistor pair can be controlled by adjusting the bias voltage applied to each photodiode using a digital-to-analog converter. The gain of each photodiode/transistor pair can be controlled based on the detected temperature of each photodiode.

BACKGROUND

Unless otherwise indicated herein, the materials described in thissection are not prior art to the claims in this application and are notadmitted to be prior art by inclusion in this section.

A light detection and ranging (LIDAR) device can detect objects in itsenvironment by transmitting light into the environment and receiving aportion of the transmitted light that has reflected from the objects inthe environment back toward the LIDAR device. The received light can bedetected by one or more photodetectors. For example, the LIDAR devicecan include an optical system that focuses the received light onto oneor more photodetectors.

SUMMARY

Some embodiments of the present disclosure provide a system including:(i) an analog-to-digital converter; (ii) at least one photodiode biasingvoltage source; (iii) a plurality of photodetector channels, whereineach photodetector channel comprises: (a) a photodiode coupled to the atleast one photodiode biasing voltage source and configured to provide aphotodiode signal indicative of light incident on the photodiode whenthe photodiode is reverse-biased by the at least one photodiode biasingvoltage source; (b) a capacitor coupled to the photodiode; and (c) atransistor that has an input coupled to the photodiode via the capacitorand an output coupled to the analog-to-digital converter and that isconfigured to amplify the photodiode signal to provide an amplifiedphotodiode signal at the output when the transistor is operationallybiased; and (iv) a channel selector that is configured to individuallyselect each respective photodetector channel in the plurality ofphotodetector channels by operationally biasing the respectivetransistor in the selected photodetector channel.

Some embodiments of the present disclosure present a method including:(i) selecting, during a first period of time, a first photodetectorchannel of a system, wherein the system includes: (1) ananalog-to-digital converter; (2) at least one photodiode biasing voltagesource; (3) a plurality of photodetector channels, wherein eachphotodetector channel includes: (a) a photodiode coupled to the at leastone photodiode biasing voltage source and configured to provide aphotodiode signal indicative of light incident on the photodiode whenthe photodiode is reverse-biased by the at least one photodiode biasingvoltage source; (b) a capacitor coupled to the photodiode; and (c) atransistor that has an input coupled to the photodiode via the capacitorand an output coupled to the analog-to-digital converter and that isconfigured to amplify the photodiode signal to provide an amplifiedphotodiode signal at the output when the transistor is operationallybiased; and (d) a channel selector that is configured to individuallyselect each respective photodetector channel in the plurality ofphotodetector channels by operationally biasing the respectivetransistor in the selected photodetector channel; wherein selecting thefirst photodetector channel includes operating the channel selector tooperationally bias the respective transistor of the first photodetectorchannel; (ii) detecting, during the first period of time, light receivedby the respective photodiode of the first photodetector channel bydetecting the output of the respective transistor of the firstphotodetector channel using the analog-to-digital converter; (iii)selecting, during a second period of time, a second photodetectorchannel of the system, wherein selecting the second photodetectorchannel comprises operating the channel selector to operationally biasthe respective transistor of the second photodetector channel; and (iv)detecting, during the second period of time, light received by therespective photodiode of the second photodetector channel by detectingthe output of the respective transistor of the second photodetectorchannel using the analog-to-digital converter.

These as well as other aspects, advantages, and alternatives, willbecome apparent to those of ordinary skill in the art by reading thefollowing detailed description, with reference where appropriate to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates an example LIDAR system in an example environment.

FIG. 1B illustrates example waveforms of emitted illumination andreceived reflected light signals of the LIDAR system of FIG. 1A.

FIG. 2 illustrates example waveforms of emitted illumination andreceived reflected light signals of an example LIDAR system.

FIG. 3A illustrates example components of a multichannel photodetectorsystem.

FIG. 3B illustrates example components of a specified impedance.

FIG. 4 is a functional block diagram of an example LIDAR system.

FIG. 5 is a flowchart of an example method.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying figures, which form a part hereof. In the figures, similarsymbols typically identify similar components, unless context dictatesotherwise. The illustrative embodiments described in the detaileddescription, figures, and claims are not meant to be limiting. Otherembodiments may be utilized, and other changes may be made, withoutdeparting from the scope of the subject matter presented herein. It willbe readily understood that the aspects of the present disclosure, asgenerally described herein, and illustrated in the figures, can bearranged, substituted, combined, separated, and designed in a widevariety of different configurations, all of which are explicitlycontemplated herein.

I. OVERVIEW

A light detection and ranging (LIDAR) system determines the distance toone or more points or objects in an environment by emitting pulses oflights to illuminate the one or more points or objects and detectinglight responsively emitted from (e.g., reflected from) the one or morepoints or objects. The LIDAR system can then determine the distance tothe one or more points or objects by determining an amount of time(e.g., a ‘time-of-flight’) between emission of a pulse of illuminationand the reception of a corresponding pulse or other feature of detectedresponsively emitted (e.g., reflected) light. Such distance informationcan be used to map the environment, to determine the locations, sizes,geometries, velocities, or other information about objects in theenvironment, or to determine some other information about theenvironment of the LIDAR system. In some examples, information about anenvironment determined by a LIDAR system could be used to control anautonomous vehicle (e.g., a driverless car) such that the autonomousvehicle can navigate the environment to reach a destination whileavoiding obstacles.

The LIDAR system could include more than one light emitter and/or morethan one photodetector. The light emitters/photodetectors could beconfigured to illuminate/receive light from one or more specifieddirections relative to the LIDAR system. The specified directions couldspan a range of directions (e.g., be regularly spaced across a range ofangles in one or more directions) such that the distance from the LIDARsystem to the environment (e.g., to objects in the environment) acrossthe range of directions could be mapped. This could allow thedetermination of the shape of the environment and/or the shape ofobjects in the environment. In some examples, the light emitters and/orphotodetectors could be actuated such that the direction toward whichlight is emitted/from which light is received can be controlled. In suchexamples, the specified direction could be scanned across a range ofangles.

A single light emitter could provide light to illuminate a variety ofpoints or objects in an environment such that more than onephotodetector could receive responsively emitted (e.g., reflected)light. In some embodiments, a LIDAR system could include a plurality oflight emitters each corresponding to a respective photodetector suchthat a particular light emitter emits light in a direction from whichthe corresponding photodetector receives light. In some examples, theLIDAR system could include optics, e.g., configured to focus a beam oflight emitted toward the environment in a specified direction and/or tofocus light received from the environment from a particular directiononto a light-sensitive element of a photodetector.

Photodetectors of a LIDAR system could include a variety of componentsconfigured in a variety of ways. In some examples, a photodetector couldinclude a reverse-biased photodiode. When a photodiode isreverse-biased, the current through the photodiode can be related to theintensity of the light received by the photodiode. In such examples, thereverse bias voltage could be sufficiently high (e.g., less thanapproximately 340 volts, in some examples between approximately 100volts and approximately 250 volts) that the photodetector operates in anavalanche mode, i.e., electrons in the photodiode generated by receivedphotons could be multiplied through avalanche multiplication due to thehigh electrical field in the photodiode. In some examples, thephotodiode could be an avalanche photodiode configured to increase thismultiplication effect (e.g., by being doped and/or beveled in such a wayto increase the amount of avalanche multiplication). The current throughthe photodiode could be amplified, switched, multiplexed, or otherwiseapplied to an analog-to-digital converter (e.g., a comparator, asigma-delta modulator) to allow a digital controller or other digitalcomputing elements to perform some operations based on the receiveddetected light (e.g., to determine a distance between the LIDAR systemand objects in the environment).

In some examples, each photodetector and/or photodiode could correspondto a respective ADC or other components. Alternatively, the outputs of aplurality of photodiodes could be applied to a single ADC (e.g., tooreduce a cost, a power consumption, a size, or to affect some otherproperty of the LIDAR system). In some examples, each photodetectorcould comprise a photodetector channel that includes a photodiode,coupling capacitor, amplifying/multiplexing transistor, transistorand/or photodiode biasing components, and/or other components. In suchexamples, the outputs of each of a plurality of such photodetectorchannels could be applied to a single ADC. Applying the outputs of aplurality of photodiodes, photodetectors, and/or photodetector channelsto a single ADC could include using a multiplexer to sequentially applya signal (e.g., a signal related to the current through the photodiodes)from each photodiode in turn to the single ADC (i.e., to sequentiallyselect each photodiode in turn). Such a multiplexer could include anumber of electronic switches, amplifiers, buffers, blocking capacitorsor other passive filtering elements, or other components. Such amultiplexer could be configured to reduce cross-talk between differentphotodiodes, i.e., to reduce an amount of signal applied to the ADC fromnon-selected photodiodes.

In a particular example, a multiplexer could include a plurality oftransistors (e.g., silicon-germanium (SiGe) bipolar transistors) eachincluded as part of a respective photodetector channel that additionallyincludes a respective reverse-biased photodiode. An output of eachphotodiode (e.g., the anode of the diode) could be coupled (e.g., via acapacitor) to the input of the corresponding transistor (e.g., to thebase of a bipolar transistor). An output (e.g., the collector) of thetransistors could be coupled to an ADC (e.g., a high-frequency ADC, acomparator). The transistors could be configured to amplify respectivephotodiode output signals when operationally biased (e.g., whenoperationally biased by applying a biasing voltage and/or currentto/through a base or gate of the transistors). A channel selector couldbe configured to individually select each transistor (e.g., to selectrespective photodetector channels including each transistor) byoperationally biasing each transistor individually (i.e., during eachpoint in time, operationally biasing a single transistor of a pluralityof transistors while not operationally biasing other transistors of theplurality of transistors).

The channel selector could operate to operationally bias a transistor byapplying a voltage and/or current to the transistor, e.g., by applying aspecified bias current through the base of a bipolar transistor byapplying a specified bias voltage to a bias resistor coupled to the baseof the bipolar transistor. The channel selector could include a CMOSgate or other type of electronic switch to connect the transistor (e.g.,the base of a bipolar transistor) via a bias resistor or othercomponent(s) to a source of the specified voltage to operationally biasthe transistor and to connect the transistor to a ground or otherlower-voltage source to not operationally bias the transistor. Further,a Schottky diode or other voltage-clamping element could be included toprevent an input to the transistor (e.g., from the photodiode) fromcausing the transistor to saturate (e.g., by preventing the voltageand/or current applied to the transistor by the photodiode fromincreasing above the specified bias voltage/current by more than aspecified amount).

A gain of a photodiode, a transistor, and/or a photodetector channel(e.g., a combination of a photodiode, a transistor, and/or otherelectronic components of a LIDAR system) could be controlled accordingto an application by controlling bias voltages and/or currents appliedto the photodiode, transistor, and/or one or more components of thephotodetector channel. For example, an amount of voltage applied to aphotodiode could be adjusted to control an overall gain of aphotodetector channel that includes the photodiode and a transistor thatcan be operationally biased by a channel selector as described above.This could include controlling a high voltage used to reverse-bias anumber of photodiodes in common (e.g., a high-voltage rail of the LIDARsystem). Additionally or alternatively, each photodiode (or othercomponent to be biased) could have a bias voltage that is individuallycontrollable, e.g., the LIDAR system could include a digital-to-analogconverter (DAC) for each of the photodiodes that is configured toprovide an independently adjustable bias voltage to each photodiode.

The gain of a photodiode and/or the overall gain of a photodetectorchannel (e.g., a photodetector channel that includes a transistor and aphotodiode, as described elsewhere herein) can be related to thetemperature of the photodiode and/or a photodiode of the photodetectorchannel. A relationship between the temperature of a photodiode, areverse bias voltage applied to the photodiode, and the gain (i.e., therelationship between the intensity of light received by the photodiodeand the magnitude of an output signal of the photodiode) of thephotodiode could be determined and used to adjust the bias voltageand/or temperature of the photodiode such that the gain of thephotodiode is controlled (e.g., such that the gain of the photodiode hasa specified value). In some examples, the temperature of the photodiodecould be detected and the bias voltage applied to the photodiode couldbe controlled based on the detected temperature such that the photodiodegain has a specified value.

Other components could be included to couple a photodiode to atransistor or other elements, to bias the photodiode, and/to prevent thephotodiode from being damaged during operation. For example, a capacitorcould be used to couple the anode or cathode of the photodiode to atransistor (or other component). The capacitance could block ahigh-voltage DC bias applied to the photodiode from being applied to thetransistors. A capacitance or some other property of the capacitor couldbe specified such that a total current passing through the photodiode asa result of receiving a pulse of light is limited. Additionally oralternatively, a resistor having a specified resistance could be coupledbetween the photodetector and a source of a bias voltage such that atotal current passing through the photodiode as a result of receiving apulse of light is limited. In a particular example, a photodiode couldbe coupled to a source of bias voltage via an approximately 300 kΩresistor and coupled to a transistor via an approximately 47 picofaradcapacitor. Such passive components (e.g., resistors, capacitors) couldbe configured to decouple certain components and/or signals, e.g., todecouple noise generated by a DAC of a bias voltage source from atransistor or other component receiving a signal from the photodiode.

Note that multiplexers, photodiodes, bias voltage sources, transistors,channel selectors, and/or other components or systems as describedherein are not limited to use in a LIDAR system. Embodiments describedherein could be applied to a variety of systems of devices wherein aplurality of photodiodes or other sensor components or other signalsources are multiplexed to provide an output to a single component(e.g., a single ADC). For example, a plurality of photodetectors couldbe used to detect light emitted from a biological sample in response toillumination (e.g., to detect emission of light by fluorophores in avariety of non-overlapping regions of a sample environment). In anotherexample, a plurality of photodetectors could be used for coincidencedetection between a number of optical signals. Other applications areanticipated.

It should be understood that the above embodiments, and otherembodiments described herein, are provided for explanatory purposes, andare not intended to be limiting.

II. EXAMPLE MULTIPLEXED PHOTODETECTORS

FIG. 1A shows an example LIDAR system 100 situated in an environmentthat includes a number of objects (e.g., an automobile, an overhang).The LIDAR system is configured to emit a plurality of beams of lightinto the environment and to receive reflected or otherwise responsivelyemitted light from the environment to determine the distance between theLIDAR system 100 and objects in the environment. The LIDAR system 100includes three light emitters 110 a-c configured to emit respectivebeams of emitted light 111 a-c in respective directions. As shown inFIG. 1A, the beams of emitted light 111 a-c illuminate respectiveportions of the environment 107 a-c. The portions of the environment 107a-c responsively reflect (or otherwise emit) light and a portion of theresponsively emitted light comprises respective reflected lights 121 a-cthat are received by respective photodetectors 120 a-c of the LIDARsystem 100.

The light emitters 110 a-c and/or photodetectors 120 a-c could includeoptics (e.g., lenses, mirrors, diffraction gratings) configured to emitlight toward/receive light from a specific direction and/or to focussuch light, to filter out one or more wavelengths, bands of wavelengths,polarizations, or other specified properties of such light, or tootherwise interact with or modify such light. For example, optics of theLIDAR system 100 could be configured to focus and/or collimate lightproduced by one or more light emitters (e.g., 110 a-c) into one or morerespective beams of light directed in respective directions toward theenvironment of the LIDAR system 100. The optics could additionally beconfigured to focus light responsively emitted from (e.g., reflectedfrom) respective regions of the environment located in respectivedirections from the LIDAR system 100 (e.g., the directions toward whichthe light emitters emitted beams of light) onto respectivephotodetectors (e.g., 120 a-c) of the LIDAR system 100. The optics couldadditionally be configured to filter wavelengths of the received lightsuch that photodetectors of the LIDAR system 100 substantially onlyreceived light corresponding to the wavelength of light emitted by thelight emitters of the LIDAR system 100 (e.g., such that thephotodetectors substantially only receive the emitted light that isreflected from objects or portions of the environment).

The light emitters include lasers, LEDs, or other light-emittingelements. The light emitting-elements could be configured to emitsubstantially monochromatic light (e.g., light having substantially asingle wavelength) and/or could emit light having some other specifiedspectral content (e.g., to allow the detection of a color or otherspectrographic information about objects or regions in the environment).The light emitters could be configured to emit light at the same time orduring different periods of time. The light emitters could be configuredto emit pulses of light, to emit light continuously, to emit lighthaving an oscillating or otherwise time-varying intensity, or accordingto some other pattern or consideration. The light emitters could emitlights having different wavelengths (or polarizations, directions ofpolarization, or some other property) such that correspondingwavelength-selective filters of corresponding photodetectors couldsubstantially only receive light from respective light-emitters.

One or more properties of the received reflected lights 121 a-c (e.g., atiming, amplitude, width, or other properties of a pulse of light in thereceived reflected lights 121 a-c corresponding to a pulse ofillumination in respective emitted lights 111 a-c) could be used todetermine the distance between the LIDAR system 100 and objects in theenvironment in directions corresponding to the directions of the emittedlights 111 a-c (e.g., the distance to objects comprising the portions ofthe environment 107 a-c). A difference between the timing of an emittedpulse of illumination and the timing of a corresponding pulse ofreceived, responsively emitted (e.g., reflected) light could be used todetermine a distance between a LIDAR system that includes the lightemitter and the photodetector (e.g., using a known speed of light in theenvironment).

As an example, FIG. 1B shows a timing diagram of pulses of illuminationof the emitted lights 111 a-c and respective received reflected lights121 a-c. Illumination waveforms 115 a-c represent the intensity ofrespective beams of emitted light 111 a-c emitted by respective lightemitters 110 a-c. Detector waveforms 125 a-c represent the intensity ofrespective reflected lights 121 a-c received by respectivephotodetectors 120 a-c. As shown in FIG. 1B, the light emitters 110 a-cemit respective pulses of light (shown in the Figure as square pulses)at substantially the same point in time (indicated by the dashed line,showing illumination time 117). Detector waveforms 125 a-c includerespective detected pulses 126 a-c corresponding to light emitted fromrespective light emitters 110 a-c during the illumination time 117 andreflected from portions of the environment 107 a-c. Detection times 127a-c can be determined from the detected pulses 126 a-c (e.g., bydetermining a peak amplitude, by determining a centroid, by determininga mean time between threshold crossings, or by using some other method).The determined detection times 127 a-c can then be used to determinedistances to respective portions of the environment 107 a-c based ontime differences between the illumination time 117 and respectivedetection times 127 a-c.

In some examples, the intensity or some other detected property of lightreceived by a plurality of photodetectors (e.g., 120 a-c) could bemultiplexed or otherwise combined and applied to a singleanalog-to-digital converter (ADC) or some other electronic device orcomponent. For example, an ADC capable of sampling at a sufficientlyhigh rate and/or having a sufficiently high bandwidth for an application(e.g., to provide samples of the received light intensity at asufficiently high temporal resolution to provide for determination ofdistances to portions of the environment at a sufficiently high spatialresolution/sensitivity) could have a size, a power requirement, a mass,a data bus width and/or output bandwidth, a cost, or some other propertysuch that a LIDAR system could include a single such ADC. In such anexample, light received from the environment (e.g., light emitted by aLIDAR system and reflected from objects or regions of an environment)could be detected by a plurality of photodetectors (e.g., by a pluralityof photodiodes) and a signal from each of the photodetectors (e.g., anelectronic output related to the intensity of light received by theindividual photodetectors) could be applied, during respective differentperiods of time (e.g., sequentially), to a single ADC.

As an illustrative example, FIG. 2 shows a timing diagram of pulses ofillumination of the emitted lights 111 a-c and a multiplexed combinationof respective received reflected lights 121 a-c. Illumination waveforms210 a-c represent the intensity of respective beams of emitted light 111a-c emitted by respective light emitters 110 a-c. Detector waveform 220represents the intensity of respective reflected lights 121 a-c receivedby respective photodetectors 120 a-c and multiplexed in time to a singlesignal (e.g., a signal applied to an ADC). As shown in FIG. 2, the lightemitters 110 a-c emit respective pulses of light (shown in the Figure assquare pulses) at respective different points in time (indicated by thedashed lines and triangles, showing respective illumination times 217a-c). The detector waveform 220 shows the time-domain-multiplexedcombination of the outputs of the photodetectors 120 a-c; that is,during different respective periods of time the detector waveform 220reflects the detected intensity (or other output signal) of respectivedifferent photodetectors 120 a-c. As shown in FIG. 2, between the first217 a and second 217 b illumination times the detector waveform 220represents the output of the first photodetector 120 a, between thesecond 217 b and third 217 c illumination times the detector waveform220 represents the output of the second photodetector 120 b, and thedetector waveform 220 represents the output of the third photodetector120 c for a period of time subsequent to the third illumination time 217c.

The detector waveform 220 includes detected pulses 226 a-c correspondingto light emitted from respective light emitters 110 a-c duringrespective illumination times 217 a-c and reflected from portions of theenvironment 107 a-c. Detection times 227 a-c can be determined from thedetected pulses 226 a-c (e.g., by determining a peak amplitude, bydetermining a centroid, by determining a mean time between thresholdcrossings, or by using some other method). The determined detectiontimes 227 a-c can then be used to determine distances to respectiveportions of the environment 107 a-c based on respective determined timedifferences 230 a-c between respective illumination times 217 a-c andrespective detection times 227 a-c. That is, longer determined timedifferences could be related to light reflected from objects or portionsof the environment that are more distant from the LIDAR system 100.

The duration of periods of time during which the detector waveform 220is related to the output of each photodetector could be specified toallow a rate of illuminating and detecting responsively reflectedreceived light from a plurality of photodetectors/light emitters. Thisrate, duration, and/or switching time could be related to a number oflight/emitter photodetector pairs included in the LIDAR system and afrequency at which the distance between the LIDAR system and theenvironment is detected/updated. Further, the photodetectors 120 a-c andlight emitters 110 a-c could be actuated to receive light from/emitlight toward the environment in different directions during differentperiods of time (e.g., the light emitters 110 a-c and photodetectors 120a-c could be actuated to rotate about an axis such that the directionsof emission/reception rotate to scan the environment around the LIDARsystem 100). In such examples, shorter time periods during which eachphotodetector output is applied to the ADC or other multiplexed outputcould allow higher rates of distance detection (e.g., by allowing theplurality of photodetector outputs to be scanned in a shorter period oftime) and/or some other increased rate, decreased latency, or otherimproved property of the LIDAR system.

In some examples, periods of time during which the detector waveform 220is related to the output of each photodetector could be separated byswitching times related to the operation of a channel selector or othercomponents to operationally bias respective transistors of thephotodetector channels. Such a switching time could be related to asettling time or other properties of transistors of the photodetectorchannels (e.g., a time following the application of a biasing currentand/or voltage to the transistors during which the output of thetransistor is changing or otherwise not indicative of the currentthrough and/or light received by a respective photodiode of aphotodetector channel). Such a switching time could additionally oralternatively be related to a value of an applied biasing voltage orcurrent, an effective capacitance and/or impedance of the transistors,an effective capacitance and/or impedance of electronic switches orother components of a channel selector that are used to apply thebiasing voltages and/or currents to operationally bias the transistors.In some examples, such switching times could be minimized, e.g., tomaximize an amount of time during which a LIDAR system (e.g., 100) couldoperate to detect (e.g., using an ADC) intensities or other propertiesof light received by photodetectors of the LIDAR system. For example, aLIDAR system (e.g., transistors of photodetector channels thereof,components of channel selectors thereof) could be configured and/oroperated such that such switching times have durations that are lessthan approximately 100 nanoseconds.

Electronics of a LIDAR system (e.g., photodetectors, multiplexers, ADCs,amplifiers, filters, light emitters, light emitter drivers, pulsegenerators, power supplies, timers, oscillators, clocks) could beconfigured in a variety of ways to allow a plurality of pulses (or otherwaveforms) of light to be emitted toward an environment from the LIDARsystem in a plurality of directions and to detect properties (e.g.,intensity waveforms, pulse timings) of responsively emitted (e.g.,reflected) light received from the environment from correspondingdirections. In some examples, this could include the LIDAR system havinga plurality of ADCs or other components configured to receive outputsfrom respective single photodetectors (i.e., the LIDAR could include asmany ADCs as photodetectors). Alternatively, the output of a pluralityof photodetectors of a LIDAR system could be multiplexed and applied toa single such ADC.

FIG. 3 illustrates electronic circuitry of a LIDAR system 300 whereinthe outputs of a plurality of photodetector channels (components of aparticular photodetector channel indicated by components within thedashed box 310, components common to the plurality of photodetectorchannels outside the dashed box) can be applied to a single ADC 380. Aparticular photodetector channel 310 includes a photodiode 330configured to receive responsively emitted (e.g., reflected) light 333and to be operated (e.g., reverse biased) such that an electrical signalof the photodiode (e.g., a current through the photodiode) is related toan intensity of the received light 333. The cathode of the photodiode330 is coupled to a photodiode voltage biasing source 305 in common withthe cathodes of photodiodes of other photodiode channels. The anode ofthe photodiode 330 is coupled to a digital-to-analog converter (DAC) 340via a resistor 385.

The anode of the photodiode 330 is also coupled to the input (e.g.,base) of a transistor 370 (e.g., a bipolar transistor) via a capacitor350. The base of the bipolar transistor 370 is also coupled to a voltageV_(SELECT) provided by a channel selector (not shown) that can becontrolled to operationally bias the transistor 370 (e.g., during one ormore specified periods of time). The input of the transistor 370 iscoupled to V_(SELECT) via a resistor 360 and a Schottky diode 365. Anoutput (e.g., collector) of the transistor 370 is connected in commonwith the outputs of transistors of other photodiode channels to the ADC380. The transistor 370 is also coupled to an electrical ground 375 ofthe LIDAR and to a transistor voltage source via a specified impedance377. The transistor 370 and components coupled thereto are configuredsuch that the transistor 370, when operationally biased, amplifies thephotodiode signal (i.e., the current signal through the photodiode 330that is related to the intensity of the received light 333) applied tothe transistor input and provides the amplified output signal to the ADC380.

The photodiode voltage biasing source 305 and DAC 340 operate to apply avoltage to reverse-bias the photodiode 330 such that the photodiode 330provides a photodiode signal (e.g., a current through the photodiode, avoltage coupled to the transistor 370 through the capacitor 350)indicative of the received light 333 incident on the photodiode 330(e.g., indicative of the intensity of the received light 333). A gain ofthe photodiode 330, i.e., a relationship between an amplitude of theproduced photodiode signal (e.g., a magnitude of a produced voltagesignal) and the received light 333 (e.g., an intensity of the receivedlight 333) could be related to the magnitude of the reverse-biasingvoltage applied to the photodiode 330, a resistance of the resistor 385,or some other factors. An increase in the magnitude of the appliedreverse-bias voltage (e.g., by increasing the voltage provided by thephotodiode voltage biasing source 305 and/or by decreasing the voltageprovided by the DAC 340) could increase the gain of the photodiode 330.In some examples, the voltage provided by the (at least one) photodiodevoltage biasing source 305 could be controllable. Note that thephotodiode voltage biasing source 305 is applied in common to aplurality of photodiode channels (including, e.g., 310); however, aplurality of photodiode voltage biasing sources could be included toprovide respective biasing voltages to respective photodiodes (e.g.,330) and/or to respective groups of photodiodes in common.

In some examples, the applied reverse-bias voltage could be sufficientlyhigh that the photodiode 330 operates in an avalanche mode, i.e.,electrons in the photodiode generated by received photons could bemultiplied through avalanche multiplication due to the high electricalfield in the photodiode. This could include the applied reverse-biasvoltage being a high voltage, e.g., a voltage between approximately 150volts and approximately 250 volts. In some examples, the photodiodecould be an avalanche photodiode configured to increase thismultiplication effect (e.g., by being doped and/or beveled in such a wayto increase the amount of avalanche multiplication).

A channel selector (not shown) is configured to individually select eachphotodetector channel (e.g., 310) of the plurality of photodetectorchannels of the LIDAR system 300 individually by operationally biasing(e.g., providing a biasing current and/or voltage via respectiveV_(SELECT) voltage sources of respective photodetector channels)respective transistors (e.g., 370) of the photodetector channels. Thiscould include providing a single biasing voltage to each of thetransistors (e.g., approximately 1 volt) applied to respective biasingresistors (e.g., approximately 5 kΩ resistors, e.g., 360). Additionallyor alternatively, the channel selector could provide a different voltageto each of the transistors to operationally bias the transistors (e.g.,a different voltage for each of the transistors specified to control theoverall gain of each of the photodetector channels). In some examples,the biasing voltage is specified to provide a specified biasing current(e.g., such that a biasing current of approximately 50 microamps passesthrough the base of the transistors). In some examples, the channelselector could, during some periods of time, operationally bias notransistors. In some examples, the channel selector could operate tooperationally bias multiple transistors simultaneously. In someexamples, the transistor 370 and other components could be configuredsuch that a switching time between a first period of time during which afirst particular transistor (e.g., 370) is operationally biased by thechannel selector and a second period of time during which a secondparticular transistor is operationally biased by the channel selector isless than approximately 100 nanoseconds.

The output of a selected individual transistor could be detected by theADC 380 to generate a variety of digital outputs in a variety of ways.In some examples, the ADC 380 could include one or more comparatorsconfigured to output a digital signal when the signal received from theselected transistor exceeds some specified voltage(s). In some examples,the ADC could be configured or operated to generate a digitalrepresentation (e.g., a number of bits representing numeric value) ofthe voltage and/or current of the signal received from the selectedtransistor at one or more points in time (e.g., at a plurality of pointsin time at a specified sample rate). In some examples, the ADC 380 couldbe configured to produce a number of such digital representations (i.e.,samples) in response to some signal (e.g., in a triggered mode) and orduring a specified period of time (e.g., during a period of time duringwhich it is expected that a pulse of increased intensity will occur inthe received light 333). Other modes of operation and outputs of the ADC380 are anticipated. The outputs of the ADC 380 could be used for avariety of applications including determining a distance to an object orportion of the environment from which the received light 333 wasreceived based on a time difference between the timing of a pulse ofincreased intensity in the received light 333 and the timing of emissionof a pulse of illumination (e.g., by a laser of the LIDAR system 300) toilluminate the environment such that the received light 333 isresponsive emitted (e.g., reflected).

The photodiode 330 could be configured in a variety of ways. Thephotodiode 330 could include silicon, germanium, indium galliumarsenide, lead sulfide, mercury cadmium telluride, or some otherlight-sensitive semiconductor material. The composition, doping, orother characteristics of the photodiode 330 could be specified tocontrol the spectral sensitivity of the photodiode 330. For example, thephotodiode 330 could be configured to be sensitive to a wavelength oflight emitted by a light emitter of the LIDAR system 300. Additionallyor alternatively, the photodetector 330 and/or the LIDAR system 300could include an optical filter or other elements such that thephotodiode signal produced by the photodiode 330 is substantiallyunrelated to wavelengths of light other than a wavelength of lightemitted by a light emitter of the LIDAR system 300 (i.e., an opticalfilter of the photodiode 330 could substantially block light ofwavelengths other that the wavelength of the emitted light). An area ofa light-sensitive region of the photodiode 330 or other characteristicsof the photodiode 330 could be specified to control a sensitivity, again, a breakdown voltage, a gain as a function of applied reverse biasvoltage, or other properties of the photodiode 330.

A resistance of the resistor 385, the capacitance of the capacitor 350,and/or properties of additional or alternative components used to couplethe photodiode 330 to source(s) of biasing voltage and/or to some othercomponents (e.g., an amplifier, a transistor, an ADC, a multiplexer, anelectronic switch) could be specified according to a variety ofapplications. In some examples, the resistor 385 and/or capacitor 350could be specified to limit a current through the photodiode 330 whenthe photodiode receives a pulse of illumination (e.g., by the intensityof the received light 333 increases) such that the photodiode signal islimited and/or such that the photodiode 330 is not damaged by suchoperation. In some examples, the resistor 385 and/or capacitor 350 couldbe specified to provide some analog filtering, e.g., to preventswitching noise or other signals produced by the DAC 340 and/orphotodiode voltage biasing source 305 from being coupled to thetransistor 370. For example, the resistor 385 could be approximately 300kΩ and the capacitor 350 could be approximately 45 nanofarads.

The DAC (e.g., 340) of each photodetector channel (e.g., 310) could beconfigured to adjust a reverse-bias voltage applied to a respectivephotodiode (e.g., 330) of the photodiode channel. In some examples, thereverse-bias voltages applied to photodetectors of the LIDAR system 300could be controlled by controlling the voltage provided by thephotodiode voltage biasing source 305. The voltage applied to aparticular photodiode (e.g., 330) could be adjusted by controlling arespective DAC (e.g., 340). In such examples, the DACs (e.g., 340)provided to adjust the reverse bias voltage of individual photodiodes(e.g., 330) could be configured to provide voltages across a specifiedrange of voltages, e.g., the DACs could be configured to adjustreverse-bias voltages applied to respective photodiodes by at leastapproximately 50 volts.

The reverse-bias voltage applied to the photodiodes could be adjusted tocontrol a gain of the photodiodes, e.g., to control a gain of aphotodiode to prevent saturation of an amplifier, to maintain amagnitude of an output of a photodiode and/or photodetector channelwithin some specified limits of an ADC or other component, to compensatefor changes in the gain of the photodiode that are related to changes intemperature, or according to some other consideration. In a particularexample, calibration data (e.g., information describing curves,surfaces, functions, or other algorithms for predicting the gain of aphotodiode and/or the overall gain of a photodetector channel as afunction of temperature, applied reverse-bias voltage, and/or some otherfactors) for the photodetector channel 310 gain relative to thereverse-bias voltage provided to the photodiode 330 and further relativeto the temperature of the photodiode 330 could be determined (e.g., byempirical testing of the gain of the photodetector channel 310 at avariety of photodiode temperatures and applied reverse-bias voltages).When operating the photodetector channel 310, the temperature of thephotodiode 330 and/or of the photodetector channel 310 could be detected(e.g., using a temperature sensor of the LIDAR system 300 that isconfigured to detect the temperature of the photodiode 330 and/or othercomponents of the LIDAR system 300 (e.g., other photodiodes)) and thereverse-bias voltage applied to the photodiode could be adjusted basedon the detected temperature and the determined calibration data (e.g.,to maintain the gain of the photodetector channel 310 at a specifiedlevel by, e.g., operating the DAC 340 and/or photodiode voltage biasingsource 305 to adjust a reverse-bias voltage applied to the photodiode330).

Note that the configuration (e.g., topology) of the photodiode-biasingelements of the photodetector channel 310 is intended as a non-limitingexample. As shown in FIG. 3A, the photodetector signal (i.e., a voltageor current related to the light received by the photodiode 330) could becoupled from the cathode of the photodiode 330 additionally oralternatively to being coupled to the anode, as shown. This couldinclude a resistor and/or capacitor being included to couple the cathodeto the transistor 370 (and/or some other component configured to receivea photodiode signal) and/or to couple the cathode of the photodiode 330to a source of reverse-bias voltage.

Note that the transistor 370 being illustrated as a bipolar transistorin FIG. 3A is intended as a non-limiting example. The transistor 370could be a field-effect transistor, a junction gate field effecttransistor, a metal-oxide-semiconductor field effect transistor. Thetype and properties of the transistor 370 (e.g., a composition of thetransistor, a gain of the transistor, a bandwidth of the transistor, again-bandwidth product of the transistor) could be specified accordingto an application; for example, the transistor 370 could be asilicon-germanium (i.e., SiGe) bipolar transistor. The transistor couldhave a high bandwidth, e.g., a bandwidth greater than approximately 42gigahertz. The polarity of the transistor 370 being NPN is intended as anon-limiting example; the transistor 370 could alternatively be a PNPtransistor. Further, the configuration (e.g., topology) of thetransistor-biasing and/or transistor-gain-setting elements of thephotodetector channel 310 is intended as a non-limiting example. Forexample, an output signal of the transistor 370 could additionally oralternatively be coupled from the emitter of the transistor 370 (e.g.,an additional or alternative specified impedance could be included tocouple the emitter of the transistor 370 to a ground or to some othervoltage source and the output signal of the transistor 370 could becoupled from the emitter). Further, each photodetector channel couldinclude more than one transistor.

The base resistor 360 could be specified relative to a voltage providedby V_(SELECT) when operationally biasing the transistor 370, propertiesof the transistor 370, a voltage provided by the transistor voltagesource (e.g., approximately 4 volts), properties of the specifiedimpedance 377, and/or other factors to set a gain of the transistor 370,to prevent saturation of the transistor 370 when operationally biased,or according to some other consideration. Further, the Schottky diode365 is provided to prevent a voltage applied to the input of thetransistor 370 (e.g., a voltage related to one or more pulses of lightreceived by the photodiode 330) from causing the transistor 370 tobecome saturated. For example, the Schottky diode 365 could beconfigured to prevent the voltage applied to the input of the transistor370 from increasing above a voltage provided by V_(SELECT) by more thana specified amount (i.e., the Schottky diode 365 could be configured toclamp the voltage applied to the input of the transistor 370). Thiscould include the Schottky diode 365 having a forward voltage drop ofapproximately 400 millivolts.

A channel selector could operationally bias (i.e., provide biasingvoltage(s) e.g., via V_(SELECT)) transistors (e.g., 370) ofphotodetector channels (e.g., 310) of the LIDAR system in a variety ofways. In some examples, the channel selector could include an electronicswitch (e.g., a pair of complementary metal-oxide-semiconductor (CMOS)field effect transistors configured to alternatively connect an outputof the electronic switch to one of two voltage sources) coupled to theinput of the transistor 370 (e.g., coupled to V_(SELECT)) and configuredto provide a biasing voltage when the photodetector channel 310 isselected. This could include the electronic switch connecting the inputof the transistor 370 to a source of a biasing voltage (e.g., a sourceof approximately 1 volt) when the photodetector channel 310 is selectedand connecting the input of the transistor 370 to a source of anon-biasing voltage (e.g., a ground of the LIDAR system 300) when thephotodetector channel 310 is not selected. The electronic switch (e.g.,the CMOS pair of transistors) for a particular transistor (e.g., 370)and any coupling components (e.g., the biasing resistor 360, theSchottky diode 365) could be located proximate to the particulartransistor to, e.g., reduce switching time (e.g., such that a switchingtime between a transistor of a first particular photodetector channelbeing operationally biased and a transistor of a second photodetectorchannel being operationally biased is less than approximately 100nanoseconds), to reduce variability in the voltage/current applied tooperationally bias the particular transistor, or according to some otherconsideration. The source of biasing voltage could be in-common acrossphotodetector channels (e.g., could be approximately 1 volt for all ofthe photodetector channels) or could be different according tophotodetector channel. In some examples, the source of biasing voltagecould be adjustable, e.g., to allow setting a gain of a transistor byadjusting a voltage level of the respective biasing voltage source.

A configuration of the transistor 370 (e.g., a composition, size,geometry, level of doping, or some other property) and/or of thespecified impedance 377 could be specified to set a gain, bandwidth,frequency response, offset, or other properties of the photodetectorchannel 310. For example, the specified impedance 377 could be aresistor having a resistance specified to set a gain of thephotodetector channel 310. One or more properties of the specifiedimpedance 377 could be specified to select a gain and bandwidth of thephotodetector channel 310 that are within a constraint set by theconfiguration of the transistor 370 (e.g., that have a product less thanthe gain-bandwidth product of the transistor 370). For example, thespecified impedance 377 could be configured such that the bandwidth ofthe photodetector channel 310 is greater than approximately 100megahertz and/or such that the gain of the photodetector channel 310 isbetween approximately 200 and approximately 300. In some examples, thespecified impedance 377 could be configured to maximize a gain of thephotodetector channel subject to a constraint, e.g., to maximize thegain of the photodetector channel while maintaining a bandwidth of thephotodetector channel 310 to be greater than approximately 100megahertz. Of configurations and considerations related to the specifiedimpedance 377 are anticipated.

In some examples, the specified impedance 377 could include a number ofresistors, capacitors, inductors, and/or other components connected in avariety of ways. For example, FIG. 3B shows an example specifiedimpedance 390 (e.g., components comprising in whole or in part thespecified impedance 377 of FIG. 3A) comprising a resistor 391 inparallel with the series combination of a resistor 393 and an inductor395. The components of the specified resistance (e.g., 377, 390) couldbe configured to provide a specified impedance spectrum, a specifiedimpedance (e.g., a specified impedance phase and/or magnitude) at one ormore frequencies, or according to some other consideration. For example,a specified impedance (e.g., 377, 390) could be configured to have animpedance of approximately 33 ohms at approximately 0 Hertz and to havean impedance of approximately 100 ohms at high frequencies (e.g.,frequencies higher than approximately 1 megahertz).

The ADC 380 could include a variety of components (e.g., comparators,oscillators, pulse generators, capacitors, integrators, electronicswitches, amplifiers) configured in a variety of ways to provide avariety of different types of digital outputs related to signalspresented to the ADC 380. For example, the ADC could include acomparator configure dot provide a high digital output when the signalprovided to the ADC 380 exceeds or is below a specified level (e.g., aspecified voltage). The ADC could include a direct-conversion ADC, asuccessive-approximation ADC, a ramp-compare ADC, a pipeline ADC, asigma-delta ADC, or some other variety of ADC configured to produce oneor more digital signals and/or values related to the value of the signalinput to the ADC 380 at one or more points in time.

Note that, while shown separately in FIGS. 3A and 3B, components of aLIDAR system could integrated into one or more integrated circuits. Forexample, the DAC 340, transistor 370, and/or other components (e.g.,385, 350, 360, 365, 377, a CMOS electronic switch configured to provideV_(SELECT)) could be integrated into a single integrated circuit that isdisposed on a substrate and electrically coupled with the photodetector330, ADC 380, and/or other components. In another example, all of thecomponents of each photodetector channel 310 (e.g., the photodetector330, DAC 385, transistor 370, and/or other components) could be formedin a single integrated circuit. Further, components from multiplephotodetector channels (e.g., multiple photodetectors, multipletransistors, the ADC 380) could be integrated in single integratedcircuit. Additionally or alternatively, one or more components of theLIDAR system 300 could be discrete components assembled on a printedcircuit board or other substrate.

A LIDAR system (e.g., 300) could be used to generate information aboutan environment (e.g., to map the environment, to detect the location,velocity, size, geometry, or other information about objects in theenvironment) to enable a variety of applications. In some examples,information about an environment could be used to control an autonomousvehicle (e.g., a driverless car) such that the autonomous vehicle cannavigate an environment to reach an objective (e.g., to move to a goallocation) while avoiding obstacles (e.g., other vehicles). Further, notethat embodiments (e.g., electronic circuitry) of the LIDAR system 300and/or other embodiments described herein could be applied to a varietyof systems or applications wherein a plurality of photodiodes or othersensor components or other signal sources are multiplexed to provide anoutput to a single component (e.g., a single ADC). For example, aplurality of photodetectors could be used to detect light emitted from abiological sample in response to illumination (e.g., to detect emissionof light by fluorophores in a variety of non-overlapping regions of asample environment). In another example, a plurality of photodetectorscould be used for coincidence detection between a number of opticalsignals. Other applications are anticipated.

III. EXAMPLE LIDAR SYSTEM

FIG. 4 is a simplified block diagram illustrating the components of adevice 400, according to an example embodiment. Device 400 may take theform of a unit configured to be mounted to a vehicle and configured toscan the environment of the vehicle (e.g., to determine the distancebetween the device 400 and the environment in a plurality ofdirections). Device 400 may take the form of a handheld or portable unitconfigured to scan an environment, e.g., to scan the geometry anddimensions of a room. Device 400 may take the form of an object-scanningdevice configured to scan an object placed within and/or proximate tothe device (e.g., by detecting the distance between the device 400 andthe object in a plurality of directions and/or by rotating or otherwisemoving the object). Device 400 may be part of some other system (e.g.,part of an automobile) such that elements of the device 400 aredistribution throughout the other system and/or are in common withelements of the other system (e.g., a controller 450 of the device 400could additionally provide controller functions for the rest of thesystem). Device 400 also could take other forms.

In particular, FIG. 4 shows an example of a device 400 having a LIDARsystem 410 that includes first 412 and second 413 photodetectorchannels, a multiplexer 415, a channel selector 416, ananalog-to-digital converter (ADC) 411, first 417 and second 418 lightemitters, a user interface 420, communication interface 430 fortransmitting data to a remote system, and a controller 450. Note that aLIDAR system could include more photodetector channels and/or lightemitters than the two illustrated in FIG. 4. The components of thedevice 400 may be disposed on a mount or on some other structure formounting the device to enable stable detection of distances to objectsand/or locations in an environment of interest, mounting to an externalsurface of a vehicle (e.g., an autonomous automobile).

Controller 450 may be provided as a computing device that includes oneor more processors 440. The one or more processors 440 can be configuredto execute computer-readable program instructions 470 that are stored inthe computer readable data storage 460 and that are executable toprovide the functionality of a device 400 described herein.

The computer readable medium 460 may include or take the form of one ormore non-transitory, computer-readable storage media that can be read oraccessed by at least one processor 440. The one or morecomputer-readable storage media can include volatile and/or non-volatilestorage components, such as optical, magnetic, organic or other memoryor disc storage, which can be integrated in whole or in part with atleast one of the one or more processors 440. In some embodiments, thecomputer readable medium 460 can be implemented using a single physicaldevice (e.g., one optical, magnetic, organic or other memory or discstorage unit), while in other embodiments, the computer readable medium460 can be implemented using two or more physical devices.

The light emitters 417, 418 are configured to emit light in respectivedirections toward an environment of the device 400 to illuminaterespective objects and/or regions of the environment. The light emitters417, 418 could include LASERs, LEDS, or other light-emitting elements.The light emitters 417, 418 could be operated to emit pulses ofillumination or illumination according to some other pattern or scheme(e.g., illumination having an oscillating intensity) such that lightresponsively emitted from the environment (e.g., reflected by therespective objects and/or regions of the environment) can be detected bythe photodetector channels 412, 413 and used to determine a distance tothe respective objects/regions of the environment and/or to provide someother application.

Both photodetector channels 412, 413 include a photodiode, a couplingcapacitor, an amplifying/multiplexing transistor in common with themultiplexer 415, transistor and/or photodiode biasing components, and/orother components. Each photodetector channel 412, 413 produces arespective channel output signal related to light received by therespective photodetector channel 412, 413, e.g., related to lightresponsively emitted from (e.g., reflected from) the environment inresponse to illumination by respective light emitters 417, 418.

The channel selector 416 is configured to operate the multiplexer 415 toindividually select each of the photodetectors 412, 413 and to apply asignal produced by the selected photodetector channel to the ADC 411such that the ADC 411 can detect some property of the produced signal(e.g., detect the value of the signal at one or more points in time,detect the timing of one or more peaks in the intensity of illuminationreceived by the photodetector channels 412, 413). This could include thechannel selector 416 individually selecting respective photodetectorchannels 412, 413 by operationally biasing the respective transistor ofthe respective photodetector channel.

Note that a device could include a subset of the elements illustratedhere, e.g., a device could lack one or both of the light emitters 417,optics 411, user interface 420, and/or some other combination ofelements. Further, a device could include multiple of one or moreillustrated elements. For example, a device could include a plurality ofphotodetector channels configured to produce respective signals relatedto light received from multiple different directions and to be selectedby the channel selector 416 (e.g., to be operationally biased by thechannel selector 416 such that the ADC 411 can detect the signalproduced by the selected photodetector channel).

The program instructions 470 stored on the computer readable medium 460may include instructions to perform any of the methods described herein.For instance, in the illustrated embodiment, program instructions 470include a controller module 472 and calculation and estimation module474.

Controller module 472 may include instructions for operating the LIDARsystem 410 to detect the distance to objects and/or regions of theenvironment of the environment of the device 400 and/or to operateaccording to some other application. This could include operating thelight emitters 417, 418 to emit pulses of light toward the environmentin respective directions during respective periods of time. Operatingthe LIDAR system 410 could include operating the channel selector 416 toindividually select photodetector channels of the LIDAR system 410(e.g., 412, 413) by operationally biasing respective transistors of theselected photodetector channels and/or of the multiplexer 415 such thata signal is produced by the selected photodetector channel and appliedto the ADC 411. Operating the LIDAR system 410 could include operatingthe ADC 411 to detect one or more properties of the signal produced bythe selected photodetector channel. In some examples, operating theLIDAR system 410 could include operating an actuator or other element(s)(not shown) of the LIDAR system 410 to control a direction of the lightemitted from the light emitters 417, 418 and/or to control a directionfrom which the photodetector channels 412, 413 receive light (e.g., to‘scan’ the light emitters/photodetector channels across a range ofangles/areas of the environment). In some examples, operating the LIDARsystem 410 could include operating a photodiode bias voltage source(e.g., a DAC of one or more of the photodetector channels 412, 413) tocontrol a gain of the photodetector channels 412, 413, e.g., based on adetected temperature of the photodetector channels 412, 413.

Calculation and estimation module 474 may include instructions foranalyzing data generated by the LIDAR system 410 to determineinformation (e.g., distance between the LIDAR system 410 and objects orregions of the environment) about the environment. In particular, thecalculation and estimation module 474 may include instructions fordetermining the timing of a pulse of illumination received by one orboth of the photodetector channels 412, 413 and/or for determining thetime difference between such a determined pulse timing and the timing ofa corresponding pulse of illumination emitted by a respective lightemitter 417, 418. The calculation and estimation module 474 mayadditionally include instructions for determining the distance from therespective light emitter 417, 418 to an aspect of the environment (e.g.,an object or region of the environment) illuminated by the respectivelight emitter based on the determined timing difference.

The controller module 472 can also include instructions for operating auser interface 420. For example, controller module 472 may includeinstructions for displaying data (e.g., pulse delay time information,distance information, environment and/or object scan data) collected bythe LIDAR system 410 and analyzed by the calculation and estimationmodule 474. Further, controller module 472 may include instructions toexecute certain functions based on inputs accepted by the user interface420, such as inputs accepted by one or more buttons disposed on the userinterface.

Communication interface 430 may also be operated by instructions withinthe controller module 472, such as instructions for sending and/orreceiving information via a wireless antenna, a wired communicationsinterface (e.g., Ethernet, CANbus) which may be disposed on or in thedevice 400. The communication interface 430 can optionally include oneor more oscillators, mixers, frequency injectors, etc. to modulateand/or demodulate information on a carrier frequency to be transmittedand/or received by the antenna. Additionally or alternatively, thecommunication interface 430 can optionally include one or moreoscillators, mixers, drivers, differential pair drivers, buffers,impedance matching components (e.g. baluns), light emitters, lightdetectors, or other components configured to drive one or moredifferential and/or single-ended wired communications interfaces and/orone or more optical (e.g., fiber-optic) communications interfaces.

The computer readable medium 460 may further contain other data orinformation, such as calibration data describing the gain or otherproperties of photodetector channels (e.g., 412, 413) of the LIDARsystem 410 as functions of applied bias voltage, photodiode temperature,or other factors. The calculation and estimation module 474 may includeinstructions for generating such calibration data and/or other datadescribing the operation of the device 400 (e.g., relationships betweendistances to objects or regions of an environment and detected timedifferences between emitted light pulses and detected reflected lightpulses) based on data collected during operation of the device 400. Suchcalibration data may also be generated and/or stored by a remote serverand transmitted to the device 400 via communication interface 430. Suchcalibration data could be generated by some external system, e.g., adevice configured to determine photodetector channel gaincharacteristics when the device 400 is manufactured.

IV. ILLUSTRATIVE METHODS FOR OPERATING A LIDAR

FIG. 5 is a flowchart of a method 500 for operating a LIDAR system. TheLIDAR system includes an (i) analog-to-digital converter (ADC), (ii) atleast one photodiode biasing voltage source, (iii) a channel selector,and (iv) a plurality of photodetector channels. Each photodetectorchannel includes (a) a photodiode coupled to the at least one photodiodebiasing voltage source and configured to provide a photodiode signalindicative of light incident on the photodiode when the photodiode isreverse-biased, (b) a capacitor coupled to the photodiode, (c) atransistor having an input coupled to the photodiode via the capacitor,having an output coupled to the ADC, and configured to amplify thephotodiode signal to provide an amplified photodiode signal to the ADCwhen the transistor is operationally biased by the channel selector. Thechannel selector is configured to individually select each respectivephotodetector channel in the plurality of photodetector channels byoperationally biasing the respective transistor of selected individualphotodetector channels.

The method 500 includes selecting, during a first period of time, afirst photodetector channel of the LIDAR system (510). This includesoperating the channel selector to operationally bias a transistor of theselected first photodetector channel. The method 500 also includes,during the first period of time, detecting light received by the firstphotodetector channel by detecting an output of the first photodetectorchannel using the ADC of the LIDAR system (520). This could includeoperating the ADC to detect values of the output of the transistor ofthe selected first photodetector channel at a plurality of points intime (e.g., to sample the output at a specified rate).

The method 500 includes selecting, during a second period of time, asecond photodetector channel of the LIDAR system (530). This includesoperating the channel selector to operationally bias a transistor of theselected second photodetector channel. The method 500 also includes,during the second period of time, detecting light received by the secondphotodetector channel by detecting an output of the second photodetectorchannel using the ADC of the LIDAR system (540). This could includeoperating the ADC to detect values of the output of the transistor ofthe selected second photodetector channel at a plurality of points intime (e.g., to sample the output at a specified rate).

The method 500 for operating a LIDAR system could include additionalsteps. In some examples, the method 500 could include illuminating theenvironment of the LIDAR system with a pulse of illumination (e.g., byoperating a light emitter of the LIDAR system), and the first or secondphotodetectors could be configured to detect a responsively emitted(e.g., reflected) pulse of illumination from the environment during thefirst or second period of time, respectively. The method 500 couldadditionally include determining a distance from such a light emitter toan illuminated aspect of the environment, e.g., based on a timedifference between the emitted pulse of illumination and a correspondingdetected pulse of light (detected, e.g., by the first or secondphotodetector channels). The method 500 could include operatingadditional photodetector channels during respective additionalrespective periods of time and/or operating the first and secondphotodetectors during respective additional periods of time. The method500 could include adjusting a bias voltage applied to a photodiode,transistor, or other element of the photodetector channels (e.g., usinga DAC of the LIDAR system) to control a gain of the photodetectorchannel based on, e.g., a detected temperature of a photodiode or otherelements of the photodetector channels.

The example method 500 illustrated in FIG. 5 is meant as anillustrative, non-limiting example. Additional or alternative elementsof the method and additional or alternative components of the LIDARsystem are anticipated, as will be obvious to one skilled in the art.

V. CONCLUSION

The particular arrangements shown in the Figures should not be viewed aslimiting. It should be understood that other embodiments may includemore or less of each element shown in a given Figure. Further, some ofthe illustrated elements may be combined or omitted. Yet further, anexemplary embodiment may include elements that are not illustrated inthe Figures.

Additionally, while various aspects and embodiments have been disclosedherein, other aspects and embodiments will be apparent to those skilledin the art. The various aspects and embodiments disclosed herein are forpurposes of illustration and are not intended to be limiting, with thetrue scope and spirit being indicated by the following claims. Otherembodiments may be utilized, and other changes may be made, withoutdeparting from the spirit or scope of the subject matter presentedherein. It will be readily understood that the aspects of the presentdisclosure, as generally described herein, and illustrated in thefigures, can be arranged, substituted, combined, separated, and designedin a wide variety of different configurations, all of which arecontemplated herein.

What is claimed is:
 1. A system comprising: an analog-to-digitalconverter; at least one photodiode biasing voltage source; a pluralityof photodetector channels, wherein each photodetector channel comprises:a photodiode coupled to the at least one photodiode biasing voltagesource, wherein the photodiode is configured to provide a photodiodesignal indicative of light incident on the photodiode when thephotodiode is reverse-biased by the at least one photodiode biasingvoltage source; a capacitor coupled to the photodiode; and a transistor,wherein the transistor has an input coupled to the photodiode via thecapacitor and an output coupled to the analog-to-digital converter, andwherein the transistor is configured to amplify the photodiode signal toprovide an amplified photodiode signal at the output when the transistoris operationally biased; and a channel selector, wherein the channelselector is configured to individually select each respectivephotodetector channel in the plurality of photodetector channels byoperationally biasing the respective transistor in the selectedphotodetector channel.
 2. The system of claim 1, wherein the respectivetransistor in each photodetector channel is a bipolar transistor.
 3. Thesystem of claim 1, wherein the respective transistor in eachphotodetector channel is a silicon-germanium transistor.
 4. The systemof claim 1, wherein the respective transistor in each photodetectorchannel is coupled to an amplifier voltage source via an amplifiersource impedance, wherein the amplifier source impedance is configuredto maximize the gain of the respective transistor of each photodetectorchannel such that the respective transistor of each photodetectorchannel operates with a bandwidth less than approximately 100 megahertzwhen the respective transistor of each photodetector channel isoperationally biased by the channel selector.
 5. The system of claim 1,wherein each photodetector channel further comprises a respectiveSchottky diode and a respective bias resistor coupled in parallelbetween the input of the respective transistor of each photodetectorchannel and the channel selector, wherein the cathode of the Schottkydiode is coupled to the channel selector, and wherein the channelselector operationally biasing a particular transistor comprisesproviding a biasing voltage to the input of the particular transistorvia the respective Schottky diode and respective bias resistor.
 6. Thesystem of claim 1, wherein the respective photodiode of eachphotodetector channel is an avalanche photodiode.
 7. The system of claim6, wherein the at least one photodiode biasing voltage source provides avoltage between approximately 150 volts and approximately 250 volts. 8.The system of claim 1, wherein the voltage provided by the at least onephotodiode biasing voltage source is controllable.
 9. The system ofclaim 1, further comprising a temperature sensor configured to detectthe temperature of at least one respective photodiode of the pluralityof photodetector channels.
 10. The system of claim 1, wherein eachphotodetector channel further comprises a respective digital-to-analogconverter coupled to the respective photodiode of each photodetectorchannel via a respective resistor, wherein each digital-to-analogconverter is configured to adjust a respective reverse-bias voltageapplied to the respective photodiode by the at least one photodiodebiasing voltage source.
 11. The system of claim 10, wherein eachdigital-to-analog converter is configured to adjust the respectivereverse-bias voltage by at least approximately 50 volts.
 12. The systemof claim 1, wherein the channel selector comprises a plurality ofelectronic switches, wherein each electronic switch of the channelselector is coupled to the input of the respective transistor of eachphotodetector channel via a respective biasing resistor, wherein thechannel selector operationally biasing the respective transistor in theselected photodetector channel comprises the channel selector operatingthe respective electronic switch to provide a biasing voltage, andwherein the respective electronic switch, respective biasing resistor,and respective transistor for each photodetector channel are physicallyproximate.
 13. A method comprising: selecting, during a first period oftime, a first photodetector channel of a system, wherein the systemcomprises: an analog-to-digital converter; at least one photodiodebiasing voltage source; a plurality of photodetector channels, whereineach photodetector channel comprises: a photodiode coupled to the atleast one photodiode biasing voltage source, wherein the photodiode isconfigured to provide a photodiode signal indicative of light incidenton the photodiode when the photodiode is reverse-biased by the at leastone photodiode biasing voltage source; a capacitor coupled to thephotodiode; and a transistor, wherein the transistor has an inputcoupled to the photodiode via the capacitor and an output coupled to theanalog-to-digital converter, and wherein the transistor is configured toamplify the photodiode signal to provide an amplified photodiode signalat the output when the transistor is operationally biased; and a channelselector, wherein the channel selector is configured to individuallyselect each respective photodetector channel in the plurality ofphotodetector channels by operationally biasing the respectivetransistor in the selected photodetector channel; wherein selecting thefirst photodetector channel comprises operating the channel selector tooperationally bias the respective transistor of the first photodetectorchannel; detecting, during the first period of time, light received bythe respective photodiode of the first photodetector channel bydetecting the output of the respective transistor of the firstphotodetector channel using the analog-to-digital converter; selecting,during a second period of time, a second photodetector channel of thesystem, wherein selecting the second photodetector channel comprisesoperating the channel selector to operationally bias the respectivetransistor of the second photodetector channel; and detecting, duringthe second period of time, light received by the respective photodiodeof the second photodetector channel by detecting the output of therespective transistor of the second photodetector channel using theanalog-to-digital converter.
 14. The method of claim 13, wherein aswitching time between the first period of time and the second period oftime has a duration that is less than approximately 100 nanoseconds. 15.The method of claim 13, further comprising: illuminating an environmentwith a pulse of illumination emitted from a light source of the system,wherein the respective photodiode of the first photodetector channel isconfigured to receive the pulse of emitted illumination reflected fromthe environment; determining the timing of a pulse of illuminationreceived by the respective photodiode of the first photodetector channelrelative to the pulse of emitted illumination based on the output of therespective transistor of the first photodetector channel detected usingthe analog-to-digital converter during the first period of time.
 16. Themethod of claim 15, further comprising: determining the distance fromthe light source to an aspect of the environment illuminated by thepulse of emitted illumination based on the determined timing of thepulse of illumination received by the respective photodiode of the firstphotodetector channel.
 17. The method of claim 13, further comprising:selecting, during a plurality of further periods of time, respectivephotodetector channels of the system, wherein selecting a respectivephotodetector channel comprises operating the channel selector tooperationally bias the respective transistor of the respectivephotodetector channel; and detecting, during the plurality of furtherperiods of time, light received by respective photodiodes of respectivephotodetector channels by detecting the output of respective transistorsof the respective photodetector channels using the analog-to-digitalconverter.
 18. The method of claim 13, wherein the first photodetectorchannel further comprises a digital-to-analog converter coupled to therespective photodiode of the first photodetector channel via a resistor,and further comprising: detecting the temperature of at least onephotodiode of the system; and adjusting, using the digital-to-analogconverter, a respective reverse-bias voltage applied to the respectivephotodiode of the first photodetector channel by the at least onephotodiode biasing voltage source based on the detected temperature. 19.The method of claim 18, further comprising: determining calibration datafor the first photodetector channel, wherein the calibration dataindicates a relationship of the gain of the first photodetector channelrelative to the reverse-bias voltage provided to the respectivephotodiode of the first photodetector channel and relative to thetemperature of the respective photodiode of the first photodetectorchannel, and wherein adjusting the reverse-bias voltage applied to therespective photodiode of the first photodetector channel by the at leastone photodiode biasing voltage source based on the detected temperaturecomprises adjusting the reverse-bias voltage applied to the respectivephotodiode of the first photodetector channel based on the detectedtemperature and on the determined calibration data.
 20. The method ofclaim 13, further comprising: detecting the temperature of at least onephotodiode of the system; and controlling the voltage provided by the atleast one photodiode biasing voltage source based on the detectedtemperature.